Shelving units, such as bookcases and room dividers, are typically of one-piece, rectangular construction having a base, support sides, a top, and a number of horizontal shelves arranged between the top and base and supported by the sides. In the past, shelves were spaced with respect to one another by either permanently affixing them in a desired position or by providing removable pegs or other supports at various heights along the sides to allow the placement of the shelves in a variety of desired positions. To vary the horizontal dimension of the arranged shelf, it has been necessary to remove or re-position an inner vertical support side and insert a new and distinct shelf of a different desired horizontal length.
For example, in U.S. Pat. No. 3,613,604, there is shown a shelf unit wherein shelf sections of fixed horizontal dimension are positioned at various heights along a wall. In U.S. Pat. No. 3,677,202, there is further shown a storage system having means for retaining shelves of fixed horizontal dimension at various heights and wherein inner vertical support walls may be removed to provide for the support of fixed shelves of a different horizontal dimension. Each of these units exhibit inherent structural limitations that prohibit the expandability and angular displacement of shelves having a predetermined horizontal dimension. U.S. Pat. No. 3,998,170, shows an adjustable wire shelf for frozen foods.
The concept of modular units, and more particularly modular furniture, has evolved to allow a user to individually arrange units in such a way as is most suitable to his or her individual taste, taking into consideration available space. The prior art in providing fixed, non-expandable units wherein the shelves are either permanently or releasably associated with fixed side supports severely limits the possible modular configurations and their adaptation to changing partial conditions.